Not applicable.
This invention relates generally to a method for reducing thermal aging in an ink jet print head and, more specifically, to a method that utilizes multiple print head standby temperatures to reduce the effects of thermal aging without significantly increasing warm-up times.
A typical color ink jet print head includes an array of ink jets that are closely spaced from one another for use in ejecting drops of ink toward a receiving surface. The typical print head also has at least four manifolds for receiving black, cyan, magenta and yellow ink for use in monochrome plus subtractive color printing. The number of such manifolds may be varied where a printer is designed to print solely in black ink, gray scale or with less than a full range of color.
In a conventional ink jet print head, each ink jet is paired with an electro mechanical transducer, such as a piezoelectric transducer (PZT). The transducer typically has metal film layers to which an electronic transducer driver is electrically connected. When a voltage is applied across the metal film layers of the transducer, the transducer attempts to change its dimensions. Because it is rigidly attached to a flexible diaphragm, the transducer bends and deforms the diaphragm, thereby causing the outward flow of ink through the ink jet.
Some ink jet print heads, such as phase change ink jet print heads, utilize inks that have melting points of 80xc2x0 C. and higher. With many of these inks, optimal jetting occurs at significantly higher temperatures, such as 120xc2x0 C. and above. Consequently, during printing the ink jets and other print head components must be maintained at or above these elevated jetting temperatures. The temperature of the ink reservoirs supplying liquid ink to the ink jets must also be maintained at or near the required jetting temperatures.
Prolonged use of an ink jet print head at elevated temperatures can alter print head performance and accelerate thermal stress or aging of the print head components. This can result in image degradation due to performance variations. For example, the drop mass of ejected ink drops can vary as the print head components are thermally conditioned over time. The positioning of the ejected ink drops on the receiving surface can also vary with thermal conditioning.
To reduce thermal stress experienced by the print head, and for energy conservation purposes, it is desirable to minimize the amount of time the print head experiences elevated temperature. In the past this need has been addressed by utilizing a single xe2x80x9cstandbyxe2x80x9d mode in which the temperatures of the print head and the ink reservoir are reduced to well below the operating temperature at selected times when the printer is not in use. For example, in the Phaser(copyright) 360 solid ink color printer manufactured by Tektronix, Inc., the assignee of the present application, the temperature of the print head during printing and in the xe2x80x9creadyxe2x80x9d condition between print jobs is about 140xc2x0 C. The printer remains in the ready condition for about four hours, and after this period enters a standby condition. In the standby condition the temperature of the print head is about 102xc2x0 C. and the temperature of the ink reservoirs is about 98xc2x0 C.
When a print head and ink reservoir are in a standby condition, the printer must raise the temperature of the print head and ink reservoir back to the operating temperature before printing can begin. This imposes an undesirable delay on the printing process. For example, the Phaser(copyright) 360 printer can require approximately five minutes to raise the temperatures of the print head and ink reservoirs from the standby condition to the operating condition.
The present invention provides a method for reducing thermal aging in an ink jet print head while avoiding significant warm-up times. The method selectively utilizes multiple print head standby temperatures to reduce the effects of thermal aging over time and minimize warm-up delays.
It is an aspect of the present invention to provide a method for reducing thermal aging in an ink jet print head.
It is a feature of the present invention that the method reduces thermal aging without significantly increasing warm-up times.
It is another feature of the present invention that the method utilizes multiple standby conditions corresponding to multiple temperatures in the print head and ink reservoirs.
It is an advantage of the present invention that the method increases print head life by reducing the average temperature the print head experiences over its lifetime.
Still other aspects of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described a preferred embodiment of this invention by way of illustration of one of the modes best suited to carry out the invention. The invention is capable of other different embodiments and its details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. And now for a brief description of the drawings.